This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
A stabilizer is an implementation used in downhole drilling operations to hold a drill string essentially concentrically in place. A stabilizer can be composed of a cylindrical body and a set of stabilizer blades that form an effective diameter similar to that of the drill string's drill bit which is nominally the same diameter as the wellbore (or borehole) when initially drilled. The stabilizer blades can help keep the drill string aligned so as to avoid unintentional sidetracking or vibrations and to reduce the contact area between the drill string and the wellbore during the drilling operation.
However, when pulling the drill string out of a wellbore after the drilling operation, the blades of a stabilizer can be at risk of being caught on an obstruction such as a debris build-up or a cuttings bed or formation ledge, which would subject the stabilizer to a downward axial force. These occurrences can cause damage to or loss of the drilling tools. Additionally, it may take several days and millions of dollars in order to safely remove a stuck drill string or in many instances, part of the drill string is permanently lost (unrecoverable) and a new wellbore must be drilled.
Several patents and pieces of literature discuss systems in which stabilizer blades can be extended or retracted. U.S. Pat. No. 5,931,239 discusses a drill string carrying a stabilizer sub above a drill bit for steering or directing drilling. The stabilizer body is rotatably carried by the stabilizer sub such that the stabilizer body remains substantially stationary relative to the borehole as the drill string rotates. At least one stabilizer blade is carried by the stabilizer body, with the stabilizer blade being radially extendable from the stabilizer body and into engagement with the sidewall of a borehole. Each stabilizer blade is extendable and retractable from the stabilizer body independently of the others. The stabilizer blades are coupled to the stabilizer body such that the stabilizer blades are capable of collapsing to a minimum radial extension if the stabilizer assembly becomes stuck in the borehole.
U.S. Pat. No. 4,491,187 discusses a surface controlled blade stabilizer apparatus, in which surface control is achieved by the alteration of internal drill string pressure to move a piston carrying an actuator for expanding stabilizer blades. The stabilizer blades are spring biased inwardly when not forced outwardly by the actuator. A barrel cam controls and guides the actuator to downward, upward, and intermediate positions, such that the blades may be expanded, retracted, or held expanded when drill string pressure is reduced. The apparatus has a full open passage to allow passage of the drilling fluid (or mud) which is not interfered with by operation of the apparatus.
U.S. Pat. No. 4,754,821 discusses a locking device for use in an adjustable drill string stabilizer that comprises a fluid reservoir provided in a first body member. The reservoir is divided into two chambers by a sealing piston secured on a second body member that is moveable relative to the first body member. The chambers of the reservoir are in fluid communication through a valve which is actuatable to close said fluid communication between the chambers, thus preventing relative movement of the body members.
U.S. Pat. No. 5,293,945 discusses a downhole adjustable stabilizer and method for use in a wellbore and along a drill string having a bit at its lower end. A plurality of stabilizer blades are radially moveable with respect to the stabilizer body, with outward movement of each stabilizer blade being in response to a radially moveable piston positioned inwardly of a corresponding blade and subject to the pressure differential between the interior or the stabilizer and the wellbore. A locking member is axially moveable from an unlocked position to a locked position, such that the stabilizer blades may be locked in either their retracted or expanded positions. In the preferred embodiment of the invention, the stabilizer may be sequenced from a stabilizer blade expanded position to a stabilizer blade retracted position by turning on and off a mud pump at the surface. The stabilizer position may be detected by monitoring the back pressure of the mud at the surface, since the axial position of the locking sleeve preferably alters the flow restriction at the lower end of the stabilizer. High radially outward forces may be exerted on each stabilizer blade by one or more radially moveable pistons responsive to the differential pressure across the stabilizer, and the stabilizer is presumed to be highly reliable and has few force-transmitting components.
U.S. Pat. No. 5,311,953 discusses a trajectory control sub for steering a drill bit that contains a lower part adjustable relative to an upper part to produce an axial bend to angularly offset the drill bit so that drilling proceeds along a curved path. Adjustable stabilizer blades are mounted on the sub and are moveable between extended positions and retracted positions. An actuator is provided which selectively maintains the drill bit in axial alignment with the section of borehole being drilled, and which is actuated to move the stabilizer blades into their retracted positions and subsequently, with the stabilizer blades in their retracted positions, to effect tilting of the lower part relative to the upper part to produce the axial bend leading to tilting of the drill bit.
These references disclose extending and retracting stabilizer blades with the use of hydraulics, an actuator, or pistons. However, at present, there is not a known uniaxial, mechanical-only stabilizer with retractable stabilizer blades in the oilfield or wellbore drilling industry.